1. Field of the Invention
This invention relates to the accurate dispensing of very small quantities of ultra-fine particles in a reproducible manner.
2. Description of the Prior Art
In the pharmaceutical industries (and also other industries), it is often necessary to accurately dispense very small quantities (order of 1 mg or less) of ultra-fine (&lt;10 mm) pharmaceutical (and other) particles on a dry basis in a reproducible manner. For example, very fine particles are administered to patients by means of inhalation. Higher potency of these new drug compounds requires much smaller doses than in previous dispensing applications. The existing equipment available commercially can only dispense an amount of the order of 5.+-.0.5 mg. It would be desirable to be able to dispense quantities of 1 mg or less with a spread of .+-.0.1 mg or less.
There is no available technology to dispense such small quantities of ultra-fine particles on a dry basis. For quantities larger than 5 mg, several types of solids feeding systems have been developed over the years. Among them are feeders designed to deliver particles at flowrates of the order of 1 kg/h for laboratory and pilot scale gas-solid reactions (e.g. combustion, gasification, catalytic reactions and metallurgical processes). The most common kind of solids feeder is the mechanical feeder such as a belt or screw conveyor. However, mechanical feeders are generally inefficient and unreliable in feeding very fine particles due to the cohesive properties of the powder which prevent free-motion of solids and lead to difficulty in transporting the powder.
A fluidized bed feeder as a non-mechanical solids feeder would have the potential to dispense smaller quantities with suitable reproducibility. While there are several types of conventional fluidized bed feeders developed, none of them is suitable for the required small quantities and ultra-fine particles. None of the reported feeders can dispense the very small quantity of fine particles of interest here.
Processing of fine particles (including nanometer particles) have been identified by governments and industries as one of the key development areas for the 21st century.
To accurately dispense ultra-fine particles, all mechanical methods would fail due to the cohesive nature of the ultra-fine particles. The existing conventional solids feeders cannot handle the small quantities of particles for drug doses of the order of 1 mg or less.